1. Field of the Invention
The present invention relates to a starter that is equipped with a planetary gear speed reduction mechanism.
2. Description of the Related Art
A planetary gear speed reduction mechanism for a starter is comprised of a sun gear, an internal gear and a plurality of planetary gears that engages the internal gear and revolve around the sun gear to transmit the revolution to an output shaft thereof. As shown in FIG. 9, an internal gear block 110 that has an internal gear 100 is prevented from rotating by an outer cylindrical member 130 or the like that is integrated with a yoke 120 of the starter motor. If it rotates, the planetary gear can not revolve around the sun gear.
In a conventional starter having the above stated planetary gear speed reduction mechanism, an end surface of an internal gear block 110 only axially abuts an end surface of a casing 160 that rotatably supports an output shaft 150 via a bearing 140. Therefore, water may leak from the gap between the two members into the inside and reach a portion around the bearing 140. In such a case, the bearing may not operate properly or seize up.
In FIG. 9, the outer cylindrical member 130 is integrated with the yoke 120. If the outer cylindrical member 130 is integrated with the casing 160, water may get into the inside from the gap between the outer cylindrical member 130 and the internal gear block 110.
The present invention has been made in view of the above problem, and an object of the invention is to prevent water from leaking between the internal gear block and the casing.
According to a main feature of the invention, a starter includes a starter motor, a planetary gear speed reduction mechanism, a casing rotatably supporting an output shaft of the speed reduction mechanism and an outer cylindrical member coupled the said casing. The planetary gear speed reduction mechanism has an internal gear block in which the internal gear is formed. The internal gear block is disposed inside the cylindrical member and spline-fitted to the casing, thereby forming a labyrinth between the internal gear block and said casing.
Therefore, the casing and the outer cylindrical member are sealed to be watertight, and the internal gear block is prevented from rotating by the spline arrangement or a rotation stopper disposed between the internal gear block and the casing.
In other words, the rotation stopper is disposed at a portion of the outer periphery of the internal gear that does not overlap the internal gear in the axial direction thereof. Accordingly, deformation of the rotation stopper may not cause the internal gear any trouble.
According to another feature of the invention, the starter may be comprised of a shock absorber having a rotary disk that rotates when a torque larger than a predetermined torque is applied thereto. In this case, the water sealing labyrinth prevents water from reaching the shock absorber, particularly, to the rotary disk. Therefore, the lifetime of the shock absorber can be improved.